In recent years, there has been development of organic semiconducting (OSC) materials in order to produce more versatile, lower cost electronic devices. Such materials find application in a wide range of devices or apparatus, including organic field effect transistors (OFETs), organic light emitting diodes (OLEDs), organic photodetectors (OPDs), organic photovoltaic (OPV) cells, sensors, memory elements and logic circuits to name just a few. The organic semiconducting materials are typically present in the electronic device in the form of a thin layer, for example of between 50 and 300 nm thickness.
The photosensitive layer in an OPV or OPD device is typically composed of at least two materials, a p-type semiconductor such as a polymer, an oligomer or a defined molecular unit, and a n-type semiconductor which is for example a fullerene derivative.
Fullerene derivatives are known in the art. See for example Hirsch, Brettreich, Fullerenes: Chemistry and Reactions, Wiley, 2005. See also for example E. Voroshazi et al., J. Mater. Chem. 2011, 21, 17345-17352; K.-H. Kim et al., Chem. Mater. 2011, 23, 5090-5095; and X. Meng, ACS Appl. Mater. Interfaces 2012, 4, 5966-5973. See also US 2010/0132782 A1, US 2012/0004476 A1, WO 2008/018931 A1, WO 2010/087655 A1 and U.S. Pat. No. 8,217,260, which disclose o-QDM (ortho-quinodimethane) fullerenes.
However, while in recent years many p-type semiconductors, mainly polymers, have been prepared to enhance the performance of an OPV device, the development of suitable fullerene derivatives for use as n-type semiconductor in OPV devices has been limited to only a few selected candidates like PCBM-C60. Also, the physical properties of the fullerene derivatives known in the art, such as solubility, light stability, thermal stability are limiting their use in commercial applications.
Thus there is still a need for fullerene derivatives which are easy to synthesize, especially by methods suitable for mass production, show good structural organization and film-forming properties, exhibit good electronic properties, especially a high charge carrier mobility, a good processability, especially a high solubility in organic solvents, and high light and thermal stability.
It was an aim of the present invention to provide fullerene derivatives that provide one or more of the above-mentioned advantageous properties. Another aim of the invention was to extend the pool of n-type OSC materials available to the expert. Other aims of the present invention are immediately evident to the expert from the following detailed description.
The inventors of this invention have found that one or more of the above aims can be achieved by providing fullerene derivatives as claimed hereinafter. These fullerene derivatives are based on o-QDM fullerene, which is substituted in both alpha-positions to the benzene ring.
It was found that the fullerene derivatives as claimed hereinafter demonstrate one or more of the improved properties as described above, especially for use in OPV/OPD applications, and are better suitable for use as n-type semiconductor in OE devices compared to the fullerene derivatives as disclosed in prior art.
U.S. Pat. No. 5,763,719 and DE 4301458 A1 disclose an o-QDM fullerene of the following formula
wherein “F” is a fullerene and R1 to R8 denote a H-atom or a substituent selected from a broad variety of meanings.
JP 2013-128001 A1 and JP 2011-238847 A1 disclose an o-QDM fullerene derivative of the following formula
wherein “FLN” is a fullerene, Ar1 is an aryl group and R1 to R4 denote a H-atom or a substituent selected from a broad variety of meanings. Again, there is only explicit written disclosure for fullerenes, and their synthesis, wherein all of R1 to R4 denote H.
S. Lu et al., Org. Letters 2013, disclose an o-QDM fullerene derivative of the following formula
wherein R2 is methyl and R1 is for example COOCH3 or CN.
Youjun He et al., J. Mater. Chem. 2012, 22, 13391, disclose o-QDM fullerene derivatives of the following formulae

However, fullerene derivatives as claimed hereinafter have hitherto not been disclosed or suggested in prior art.